System and method of dewatering dredge spoils using sloping drain barge

ABSTRACT

An apparatus for dewatering dredge spoils includes a floating barge having a planar upper surface or deck. One end of the barge, such as the stem, is partially flooded or otherwise ballasted so that the deck slopes downwardly from the bow toward the stem. Dredge spoils removed from a waterway are deposited onto the bow where they flow down toward the stem. A plurality of concrete blocks on the deck form an attenuator that, in turn, defines one or more settling ponds on the surface of the barge. A weir across the stem of the barge forms an additional settling pond at the rear of the barge. Solids suspended in the water removed from the waterway settle out onto the deck when the dredge spoils are deposited onto the bow. Remaining solids suspended in the water deposit onto the deck as the water flows through the settling ponds. The relatively clear water that remains then flows back into the waterway off the stem of the sloped barge after passing through the settling ponds. Because the apparatus and method use materials and equipment, such as the barge and blocks, that are already likely to be on hand, the method and apparatus are particularly economical and easy to implement.

FIELD OF THE INVENTION

This invention relates generally to dredging equipment and moreparticularly to devices and methods for separating and collecting thesolid components of dredge spoils.

BACKGROUND OF THE INVENTION

Dredging is a common operation wherein bottom materials, such as mud,sand and sediment, are removed from a waterway. Dredging can beperformed for a number of reasons, such as increasing the depth of aharbor, channel or river to permit the safe passage of deep-draftvessels. Dredging can also be performed to permit the recovery ofminerals or other valuable raw materials from areas that are underwater.In addition, dredging can be used to remove contaminated sediments frompolluted harbors and rivers as part of a remedial clean-up operation.

Typically, dredging is performed by means of a crane operated bucketthat is repeatedly raised and lowered into the water to scoop up bottommaterials and bring them to the surface for removal. Other forms ofdredging can be accomplished using pumps to remove bottom materials andpump them to the surface in a water-based slurry. Whatever the purposeor method, dredging operations inherently create the problem of what todo with the “spoils” created as mud, sand, sediment and other materialsare removed from the bottom and brought to the surface.

Typically, water makes up a large part of the dredge spoils. The goal ofdredging, however, is not to remove water from the waterway but, rather,solids from the bottom. The water is brought up as an unavoidableconsequence inherent in the dredging operation itself. Unlesscontaminated by the dredging operation itself, it is most economical andpractical to return the water component of the dredge spoils to thewaterway after removing the solid components. This is most economicaland practical if it can be carried out on site without necessitatingtransportation of the spoils over long distances. A variety oftechniques have, therefore, been developed for dewatering dredge spoilsin dredging operations. Although effective, such techniques have leftroom for improvement in terms of simplicity, efficiency and economy.

SUMMARY OF THE INVENTION

The invention provides a system for dewatering dredge spoils including asloping, generally planar surface having an uphill end and a downhillend, and an attenuator between the uphill end and the downhill enddefining a settling pond on the surface.

The invention also provides a method of dewatering dredge spoilscomprising the steps of providing a sloping, generally planar surfacehaving an uphill end and a downhill end, providing an attenuator on thesurface between the uphill end and the downhill end to form a settlingpond on the surface, and depositing the dredge spoils onto the uphillend of the surface upstream of the attenuator so that solid componentsof the dredge spoils settle out and are deposited onto the planarsurface as liquid component of the dredge spoils flow along the surfacetoward the downhill end.

The invention also provides a sloping dredge barge for dewatering dredgespoils, comprising a floating barge having a generally planar uppersurface. The barge is ballasted so that the upper surface slopes from anuphill end to a downhill end. A plurality of blocks disposed along theupper surface form an attenuator defining a first settling pond on theupper surface upstream of said attenuator. A plurality of blocks form aweir adjacent the downhill end and define a second settling pondupstream of the weir and downstream of the attenuator. Solid componentsof the dredge spoils deposited onto the surface adjacent the uphill endsettle out and are deposited onto the planar surface as liquid componentof the dredge spoils flow through the settling ponds toward the downhillend.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the present invention that are believed to be novel areset forth with particularity in the appended claims. The invention,together with the further objects and advantages thereof, may best beunderstood by reference to the following description taken inconjunction with the accompanying drawings, wherein like referencenumerals identify like elements and wherein:

FIG. 1 is a perspective view of the upper surface of a preferredembodiment drain barge having an upper surface configured for dewateringdredge spoils, showing the dredge spoils shortly after being depositedthereon.

FIG. 2 is a perspective view of the drain barge shown in FIG. 1, showingthe dredge spoils after they have flowed down the surface of the barge.

FIG. 3 is a sectional view of the drain barge illustrated in FIG. 2.

FIG. 4 is an enlarged sectional view, similar to FIG. 3, showing thedredge spoil accumulation at the rear of the drain barge illustrated inFIG. 2.

FIG. 5 is a top plan view of an alternative embodiment drain barge,similar to that shown in FIG. 1, showing a skimmer structure at the rearof the barge.

FIG. 6 is a perspective view, similar to FIG. 1, of an alternativeembodiment drain barge.

FIG. 7 is a perspective view, similar to FIG. 2, showing the alternativeembodiment drain barge after dredge spoils have flowed down the surfaceof the barge.

DETAILED DESCRIPTION

Referring to the drawings and in particular to FIG. 1, an apparatus 10for dewatering dredge spoils 12 is illustrated. As used herein, the term“dredge spoils” will be understood to mean materials that are removedfrom a waterway during dredging operations. Regardless of the particularwaterway and bottom involved, and regardless of the purpose for whichthe dredging operation is being carried out, the dredge spoils will beunderstood to contain both a liquid component 14, such as water, and asolid component 16, such as mud, silt or sand, suspended in the liquid.The general function of the dewatering apparatus 10 and method shown anddescribed herein, is substantially to separate the solid components 16of the dredge spoils from the liquid component 14. The liquid component14 can then be returned to the waterway while the solid components 16are collected for disposal elsewhere. It will be understood that theseare relative terms, and that in practice, the complete separation of thesolid and liquid components of the dredge spoils will most likely not beachieved.

In the preferred embodiment illustrated in FIGS. 1-4, the apparatus 10provides a generally planar, generally horizontal surface 18 that isimpervious to water and sufficiently rigid and durable to withstandhaving dredge spoils 14 deposited thereon. The surface 18 is gentlyinclined so as to form an uphill end 20 and a downhill end 22. Thedredge spoils 14 removed from the waterway during the dredging operationare deposited onto the uphill end 20. They then flow along the surfacetoward the downhill end 22. A pair of sidewalls 24, 26 along the sidesof the surface 18 help confine the dredge spoils 14 for flow from theuphill end 20 toward the downhill end 22.

As further illustrated, an attenuator structure 28 is provided acrossthe surface 18 between the uphill and downhill ends 20, 22. Theattenuator 28 functions to partially restrict or attenuate the flow ofthe dredge spoils 14 from the uphill end 20 to the downhill end 22. Thishas the effect of causing the dredge spoils 14 to pool or collect alongthe portion of the surface 18 uphill of the attenuator 28. A firstretention area or settling pond 30 is thus formed on the portion of thesurface 18 uphill of the attenuator 28. By slowing the flow over thesurface 18, the solid components 16 of the dredge spoils are given anopportunity to settle out onto the surface 18. Relatively clear water isleft behind.

In the illustrated embodiment, the attenuator 28 is preferably formed ofa plurality of elements 32, referred to herein as ecology blocks,arranged to form a wall-like baffle, dam or barrier across the surface18. Unlike a true wall or dam, the attenuator 28 permits liquid flow,and its function is to slow, rather than totally restrict, the flow fromthe uphill end 20 of the surface 18 to the downhill end 22. To this end,the blocks 32 are placed in close proximity to each other, but with agap between adjacent blocks to permit the desired flow. In theillustrated embodiment, the blocks 32 are substantially rectangular inform and are arranged in two closely spaced, parallel rows of blocksplaced end-to-end across the surface 18. Preferably the blocks 32 areformed of concrete although other materials can be used.

In the illustrated embodiment, the apparatus 10 further includes an endbarrier or weir 34 extending substantially across the width of thedownhill end 22. The weir 34, in conjunction with the sidewalls 24, 26,forms an additional settling pond 36 for drain water at the downhill end22 of the surface 18.

In use, dredge spoils 12 are deposited onto the uphill end 20 of thedewatering apparatus 10 after being brought up from the bottom of thewaterway. The heavier solid components 16, which often make up the bulkof the solids removed from the waterway bottom, immediately settle ontothe surface 18 where the dredge spoils are initially deposited. Afterseveral bucketfuls of dredge spoils are deposited, a pile of solids willaccumulate. Eventually, they can be removed by means of a clamshellbucket, a bucket loader or similar earth-moving apparatus. The watercomponent 14 of the dredge spoils 12 drains off and begins flowingdownwardly toward the lower, downhill end 22 under the force of gravity.Although the bulk of the solids 16 deposit out onto the surface 18relatively quickly, the lighter components remain suspended and arecarried along by the water 14 toward the downhill end 22. It isdesirable to remove much of these remaining suspended solids beforereturning the water 14 back to the waterway.

In the illustrated embodiment, the water along with the remainingsuspended solids flows into the first settling pond 30 defmed by theattenuator 18. The reduced flow rate caused by the attenuator 28 slowsthe water 14 thereby permitting many of the still-suspended solids 16 tosettle out onto the surface 18. These solids 16 tend to accumulateagainst the blocks 32 making up the attenuator 28. The water 14 and anyremaining solids 16 still suspended therein flow around and between theindividual blocks 32 and continue downwardly along the inclined surface18 toward the weir 34 and into the second settling pond 36.

By the time the dredge spoils 12 reach the weir 34, the bulk of thesolids 16 have settled out onto the surface 18 leaving relatively clearwater 14 behind. The relatively clear water 14 then passes through theweir 34 and flows off the downhill end 22 of the surface 18 back intothe waterway.

The solids 16 that are deposited onto the surface 18 can, from time totime, be removed by various conventional means, such as clamshellbuckets, bucket loaders and shovels. Removal of the solids isfacilitated by the fact that they tend to accumulate more deeply alongthe attenuator 28, the side walls 24, 26 and the weir 34.

Preferably, the dewatering apparatus 10 and method are implemented inthe form of a floating barge having a planar upper deck which forms thesurface 18. The barge can be towed to the area of the dredging operationand anchored or otherwise secured in place. Preferably, the bargeincludes one or more ballast tanks 38 (FIGS. 3 and 4) that can beflooded as needed to lower one end, such as the stern, relative to theother, such as the bow. When so ballasted, the bow forms the uphill end20 of the surface 18 while the stem forms the downhill end 22. To avoidcorrosion, the barge is preferably ballasted with fresh rather than saltwater. The sidewalls 24, 26 can be formed by a plurality of steel platespositioned along the sides of the barge.

On advantage to using barges for this purpose is that they typicallyalready include the planar upper surface 18 or deck and the ballasttanks 38, and, therefore, require little if any modification for use inthe dewatering method. Furthermore, the slope of the deck can, withinlimits, be adjusted by controlling the amount of ballasting to controlhow quickly or slowly the dredge spoils flow along the inclined surface18.

In the illustrated embodiment, the weir 34 is preferably formed ofconcrete or other blocks 40 laid end-to-end. The blocks may or may notbe the same as the blocks 32 making up the attenuator 28. Sufficientspace exists between the blocks 40 for water 14 to flow through the weir34 and off the end 22 of the surface 18 back into the waterway. Again,the weir 34 slows the flow sufficiently to cause the water to pool inthe settling pond 36 formed immediately upstream of the weir 34, therebygiving suspended solids 16 an opportunity to settle out. Preferably, theblocks 40 are covered with a filtering element, such as a filter cloth42, to provide additional filtering before the water 14 is returned tothe waterway. Although not critical, a suitable cloth for this purposeis a geotextile fabric available through Northwest Linings of (location)under product (name). Preferably, the cloth 42 is positioned along theinboard face and tops of the blocks 40 and is held in place throughwater saturation and accumulated dredge spoil solids 16. The placementand form of the filter cloth 42 is not critical, the goal being toprovide additional filtering before the water 14 is returned to thewaterway.

Still additional filtering can be provided by positioning straw bales orsimilar material alongside the weir 34. The bales, as well as the filtercloth 42, can be replaced as needed as they get clogged with debris andsediment. Accumulated sediment in the second settling pond 36 is removedfrom time-to-time as needed.

It will be appreciated that the apparatus 10 and the method itimplements provide an efficient and economical way of dewatering dredgespoils 12. The dredge spoils 12 need only be deposited onto the uphillend 20 of the surface 18 as they are removed from the waterway.Thereafter, gravity causes the spoils 12 to flow along the inclinedsurface 18. The relatively clear water 14 that results automaticallyflows back into the waterway after the bulk of the solids 16 settle outonto the surface 18.

The attenuator structure 28 shown in FIGS. 1-4 is preferred because itis effective in slowing the flow, is easy to implement and makes removalof the accumulated solids 16 easy using a clamshell bucket. It will beappreciated, however, that this attenuator structure 28 is not the onlystructure that can be used and that other structures and configurationscan be used as well. Examples of such alternatives are shown in FIGS.5-7. It will be understood that these alternative embodiments, too, aremeant to be illustrative, rather than limiting, and that still otherconfigurations can be used without departing from the spirit and scopeof the invention in its broader aspects.

In the embodiment shown in FIG. 5, a skimmer structure 44 is provided inconjunction with the weir 34. The skimmer 44 extends upwardly from thesurface 18 upstream of the weir 34 and helps trap floating debris andother contaminants that may be on the surface of the water 14.Preferably, the skimmer 44 is formed of 2×4 lumber that rests on thesurface 18. If desired or needed, supports 46 for supporting the skimmer44 can also be provided.

In the embodiment shown in FIGS. 6 and 7, an opening 48 is provided inthe center of the weir 34 and a skimmer 44 is provided around theopening 48 as shown. As in the embodiment shown in FIG. 5, the skimmer44 functions to trap and retain debris floating on the water 14 and keepit from flowing through the weir 34. As further illustrated, two or moreattenuators 50, 52 are provided in place of the single attenuator 28used on the embodiment of FIGS. 1-4. Preferably, the attenuators 50, 52are formed by separate concrete blocks, that can be the same as theblocks 32 used in the embodiment shown in FIGS. 1-4, laid end-to-end.The blocks 32 can be positioned on the surface 18 as desired to createbaffles of differing sizes, shapes and orientations.

In FIGS. 6 and 7, neither of the attenuators 50, 52 extends fully acrossthe surface 18. Instead, the upstream attenuator 50 extends from theright sidewall 26 across the surface 18, while the downstream attenuator52 extends inwardly along the surface 18 from the left sidewall 24. Eachof the attenuators 50, 52 terminates short of the opposite side, therebyleaving a gap 54, 56. In the illustrated embodiment, the upstreamattenuator 50 includes a lip 58 to help contain accumulated solids 16.Water 14 flowing downwardly along the surface 18 first encounters theupstream attenuator 50 and flows along it until reaching the gap 54. Thewater 14 flows through the gap 54 and then downwardly along the surface18 until it encounters the downstream attenuator 52. The water 14 flowsalong the downstream attenuator 52 until reaching the second gap 56, atwhich point it flows into the settling pond defined by the weir 34. Thetwo attenuators 50, 52 thus slow the water flow along the surface 18thereby allowing the suspended solids 16 to settle out. The solids tendto accumulate along the attenuators 50, 52 where they can, from time totime, be removed as needed.

Again, it will be appreciated that the number, size, orientation andshape of the attenuators 50, 52 is not critical to the invention in itsbroader aspects and that these variables can be adjusted depending uponsuch considerations as the size of the barge, the slope of the surface,the nature of the dredge spoils and the degree of dewatering desired.

One advantage of using concrete, straw bales or other blocks to form theattenuators and weir is that they are relatively inexpensive, durableand easily obtained. Additionally, they can be easily moved around onthe surface of the sloping barge as needed to form the most effectivedewatering arrangement based on local conditions. Although concreteblocks are preferred, it will be appreciated that the invention is notlimited to such elements and that other forms of attenuator and/or weirstructures can be used, the principal requirement being that they slowthe flow of dredge spoils and facilitate the accumulation of solids onthe surface.

While a particular embodiment of the invention has been shown anddescribed, it will be apparent to those skilled in the art that changesand modifications can be made without departing from the invention inits broader aspects, and, therefore, the aim in the appended claims isto cover all such changes and modifications as fall within the truespirit and scope of the invention.

1. An apparatus for dewatering dredge spoils, comprising: a sloping,generally planar surface having an uphill end and a downhill end; and anattenuator between said uphill end and said downhill end defining asettling pond on said surface.
 2. An apparatus as defined in claim 1wherein said generally planar surface comprises the deck of a floatingvessel.
 3. An apparatus as defmed in claim 2 wherein said floatingvessel comprises a barge.
 4. An apparatus as defined in claim 3 whereinsaid barge is ballasted at one end to create said sloping surface.
 5. Anapparatus as defined in claim 1 further comprising a weir adjacent saiddownhill end.
 6. An apparatus as defined in claim 5 wherein a firstsettling pond is defmed between said attenuator and said uphill end anda second settling pond is defined between said attenuator and said weir.7. An apparatus as defined in claim 6 wherein said attenuator is formedby a plurality of elements placed adjacent each other to form awall-like structure.
 8. An apparatus as defmed in claim 7 wherein saidelements comprise individual blocks.
 9. An apparatus as defmed in claim8 wherein said blocks are formed of concrete.
 10. An apparatus as defmedin claim 8 wherein said attenuator comprises a row of said blocksarranged in a substantially straight line extending substantiallyperpendicularly across said surface.
 11. An apparatus as defmed in claim10 wherein said attenuator comprises two substantially parallel rows ofsaid blocks extending substantially perpendicularly across said surface.12. An apparatus as defmed in claim 11 wherein said blocks are spacedapart from each other to permit water flow between adjacent ones of saidblocks.
 13. An apparatus as defmed in claim 5 wherein said weircomprises a plurality of elements positioned adjacent one another toform a wall-like structure adjacent said downhill end of said surface.14. An apparatus as defined in claim 13 wherein said weir furtherincludes a filter structure adjacent said elements.
 15. An apparatus asdefmed in claim 14 wherein said filter structure comprises filter clothdisposed adjacent said elements.
 16. An apparatus as defmed in claim 15further comprising additional filtering elements adjacent said weir. 17.An apparatus as defined in claim 16 wherein said additional filteringelements comprise straw bales adjacent said weir.
 18. An apparatus asdefined in claim 13 wherein said weir includes an opening and wherein askimmer is positioned around said opening to trap floating debris. 19.An apparatus as defined in claim 5 further comprising a plurality ofsaid attenuators spaced from each other in the direction from saiduphill end to said downhill end.
 20. An apparatus as defined in claim 5further including side walls adjacent said surface for confining fluidflow substantially between said uphill and said downhill ends of saidsurface.
 21. A method of dewatering dredge spoils comprising the stepsof: providing a sloping, generally planar surface having an uphill endand a downhill end; providing an attenuator on said surface between saiduphill end and said downhill end to form a settling pond on saidsurface; and depositing the dredge spoils onto said uphill end of saidsurface upstream of said attenuator so that solid components of thedredge spoils settle out and are deposited onto the planar surface asliquid component of the dredge spoils flow along said surface towardsaid downhill end.
 22. A method as defined in claim 21 wherein said stepof providing a sloping, generally planar surface includes the step ofproviding a floating vessel having a substantially horizontal deck andpositioning the vessel with one end lower than the other so that saiddeck is inclined from the higher end to the lower end.
 23. A method asdefmed in claim 22 wherein the floating vessel is a barge and whereinsaid step of positioning the vessel includes the step of ballasting thebarge to sink one end of the barge lower into the water than the other.24. A method as defined in claim 21 wherein said step of providing anattenuator includes the step of positioning a plurality of elementsadjacent one another on the planar surface.
 25. A method as defined inclaim 21 comprising the ftrther step of returning the liquid componentof the dredge spoils to the waterway after the solid components of thedredge spoils have settled onto the planar surface.
 26. A method asdefined in claim 25 comprising the further step of removing the solidcomponents of the dredge spoils from the planar surface after the solidcomponents have settled onto the planar surface.
 27. A sloping dredgebarge for dewatering dredge spoils, comprising: a floating barge havinga generally planar upper surface, said barge being ballasted so thatsaid upper surface slopes from an uphill end to a downhill end; aplurality of blocks disposed along said upper surface to form anattenuator defining a first settling pond on said upper surface upstreamof said attenuator; and a plurality of blocks forming a weir adjacentsaid downhill end and defining a second settling pond upstream of saidweir and downstream of said attenuator, whereby solid components of thedredge spoils deposited onto said surface adjacent said uphill endsettle out and are deposited onto the planar surface as liquid componentof the dredge spoils flow through said settling ponds toward saiddownhill end.
 28. A sloping dredge barge as defined in claim 27 furthercomprising one or more tanks for ballasting said barge to create saiddownhill end.
 29. A sloping dredge barge as defined in claim 28 whereinsaid weir includes a filtering element adjacent said blocks.
 30. Asloping dredge barge as defined in claim 29 wherein said filteringelement comprises a filter cloth disposed over said blocks forming saidweir.
 31. A sloping dredge barge as defined in claim 28 furtherincluding side walls adjacent the sides of said barge for confining themovement of dredge spoils between said uphill and downhill ends of saidbarge.
 32. A sloping dredge barge as defined in claim 31 furtherincluding an an opening in said weir and a skimmer around said weir forrestraining floating debris from passing through said opening.